Project Summary Adolescent idiopathic scoliosis (AIS) is a twisting condition of the spine and is the most common pediatric musculoskeletal disorder, affecting 3% of children worldwide. Children with AIS risk severe disfigurement, back pain, and pulmonary dysfunction later in life. Girls requiring treatment for AIS outnumber boys by more than five-fold. AIS is treated symptomatically rather than preventively because the underlying etiology is unknown. Hospital charges for AIS surpass one billion dollars annually in the U.S. and are rising significantly faster than for other pediatric procedures. Our overall purpose is to understand the biologic causes of AIS as a means to early diagnosis, prevention and non-invasive biologic treatment. AIS is a complex genetic disease. Genome wide association studies (GWAS) by our group and others have identified AIS-associated regions harboring presumed regulatory sequences. For example, with our Project 3 (Genomics) collaborators we have recently shown that AIS-associated variants disrupt a putative enhancer of the PAX1 gene that is known to participate in spinal development. We also demonstrated that this locus is specifically associated with AIS in females. While these GWAS has yielded loci worthy of further study, they cumulatively account for <5% of the total genetic risk in AIS. In this Project we propose new approaches to identify the genes and mutations expected to convey substantial disease risk. In one approach we will perform exome-focused GWAS in our collection of 2,750 AIS cases and >20,000 population controls to discover disease-associated mutations in AIS candidate genes and their regulatory elements. In our second approach we will perform whole genome sequencing (WGS) in trios with affected males to discover mutations expected to convey strong disease risk. Selected genes and regulatory sequences will be characterized further by genome editing in zebrafish (Project 2) and enhancer studies (Project 3). We will define the mutational burden in AIS by large-scale re-sequencing of candidate genes and regulatory regions discovered in this project by GWAS, as well as those discovered by in Projects 2 and 3. For example, our Project 2 (Zebrafish) collaborators have discovered that multiple alleles of kif6 produce an AIS phenotype in zebrafish, prompting us to add this gene to our candidate list. For our mutation screens we will re-sequence at least 4,000 AIS cases and controls using our established method of molecular inversion probe-based targeting and massively parallel sequencing. To provide critical reagents for hypothesis-driven functional analysis of AIS, we will simultaneously expand our existing biobank of DNA, cells, tissues, and surgical samples from patients ascertained in pediatric orthopaedic centers. Finally, for patients with defined AIS-causing mutations, we will team with clinical experts in AIS to evaluate potential phenotypic correlations that may define clinical subtypes. By synergizing with other projects in the program we will define a substantial fraction of the genetic risk in AIS and establish important tools for characterizing the underlying disease mechanisms.